The ever-increasing world population and the dwindling supply of arable land available for agriculture fuels research towards developing plants with increased biomass and yield. Conventional means for crop and horticultural improvements utilize selective breeding techniques to identify plants having desirable characteristics. However, such selective breeding techniques have several drawbacks, namely that these techniques are typically labor intensive and result in plants that often contain heterogeneous genetic components that may not always result in the desirable trait being passed on from parent plants. Advances in molecular biology provide means to precisely modify the germplasm of plants. Genetic engineering of plants entails the isolation and manipulation of genetic material (typically in the form of DNA or RNA) and the subsequent introduction of that genetic material into a plant. Such technology has the capacity to deliver crops or plants having various improved economic, agronomic or horticultural traits.
Traits of interest include plant biomass and yield. Yield is normally defined as the measurable produce of economic value from a crop. This may be defined in terms of quantity and/or quality. Yield is directly dependent on several factors, for example, the number and size of the organs, plant architecture (for example, the number of branches), seed production, leaf senescence and more. Root development, nutrient uptake, stress tolerance, photosynthetic carbon assimilation rates, and early vigor may also be important factors in determining yield. Optimizing the abovementioned factors may therefore contribute to increasing crop yield.
An increase in seed yield is a particularly important trait since the seeds of many plants are important for human and animal consumption. Crops such as corn, rice, wheat, canola and soybean account for over half the total human caloric intake, whether through direct consumption of the seeds themselves or through consumption of meat products raised on processed seeds. They are also a source of sugars, oils and many kinds of metabolites used in industrial processes. Seeds contain an embryo (the source of new shoots and roots) and an endosperm (the source of nutrients for embryo growth during germination and during early growth of seedlings). The development of a seed involves many genes, and requires the transfer of metabolites from the roots, leaves and stems into the growing seed. The endosperm, in particular, assimilates the metabolic precursors of carbohydrates, oils and proteins and synthesizes them into storage macromolecules to fill out the grain. An increase in plant biomass is important for forage crops like alfalfa, silage corn and hay. Many genes are involved in the metabolic pathways that contribute to plant growth and development. Modulating the expression of one or more such genes in a plant can produce a plant with improved growth and development relative to a control plant, but often can produce a plant with impaired growth and development relative to a control plant. Therefore, methods to improve plant growth and development are needed.
Transcription factors are genes whose expression modulates the expression of other genes. This is often accomplished by the transcription factor protein binding to genomic DNA at a particular location or locations. This binding may recruit additional proteins that up- or down-regulate the expression of gene(s) nearby the transcription factor binding site. Alternatively, the binding of the transcription factor to DNA may physically slow or prevent transcription of nearby gene(s) by interfering with proteins such as RNA polymerase that are involved with transcription. Because individual transcription factors may affect the expression of multiple genes of interest, modulating transcription factor expression has the potential to simultaneously modulate the expression of multiple genes in the organism of interest, such as genes that are involved in the metabolic pathways that contribute to plant growth and development. Modulating the expression of one or more transcription factors that participates in regulating the expression of genes whose expression affects plant growth and development may improve plant growth and development, but often can produce a plant with impaired growth and development relative to a control plant. Therefore, methods to modulate transcription factor expression that can result in improved plant growth and development are needed.